This document describes how user agents determine the names and descriptions of accessible objects from web content languages. This information is in turn exposed through accessibility APIs so that assistive technologies can identify these objects and present their names or descriptions to users. Documenting the algorithm through which names and descriptions are to be determined promotes interoperable exposure of these properties among different accessibility APIs and helps to ensure that this information appears in a manner consistent with author intent.

The accessible name and description computation specification defines support that applies across multiple content technologies. This includes accessible name and description provided by general-purpose WAI-ARIA [[WAI-ARIA]] roles, states, and [=ARIA/properties=] as well as features specific to individual content languages.

This document updates and will eventually supersede the accessible name and description guidance in the Accessible Name and Description Computation 1.1 [[ACCNAME-1.1]] W3C Recommendation. It is part of the WAI-ARIA suite described in the WAI-ARIA Overview.

Introduction

User agents acquire information from the DOM [[DOM]] and create a parallel structure called the accessibility tree, made up of accessible objects. An accessible object provides information about its role, states, and [=ARIA/properties=]. An example is an accessible object whose role is menuitem, is currently in an enabled state, with a haspopup property, indicating that it leads to a sub-menu.

The two properties of accessible objects described in this document are its accessible name and accessible description. The name is a short label that provides information about the purpose of the object. An example of an accessible name for a menu item is New, signifying that the menu item provides for the creation of new documents, windows, and so on.

The description is a short explanation that further clarifies the nature of the accessible object. It is not always necessary to provide a description if the name is sufficient, but it can help a user better understand the use of the object.

Accessibility APIs currently support flat, unstructured strings for accessible names and descriptions. The result of the name/description computation is thus a flat string.

The terms "accessible name" and "accessible description" are used to emphasize that they are properties of accessible objects as exposed by Accessibility APIs. However, they are frequently referred to hereafter as simply "name" and "description".

Important Terms

While some terms are defined in place, the following definitions are used throughout this document.

Assistive Technologies

Hardware and/or software that:

  • relies on services provided by a user agent to retrieve and render Web content
  • works with a user agent or web content itself through the use of APIs, and
  • provides services beyond those offered by the user agent to facilitate user interaction with web content by people with disabilities

This definition may differ from that used in other documents.

Examples of assistive technologies that are important in the context of this document include the following:

  • screen magnifiers, which are used to enlarge and improve the visual readability of rendered text and images;
  • screen readers, which are most-often used to convey information through synthesized speech or a refreshable Braille display;
  • text-to-speech software, which is used to convert text into synthetic speech;
  • speech recognition software, which is used to allow spoken control and dictation;
  • alternate input technologies (including head pointers, on-screen keyboards, single switches, and sip/puff devices), which are used to simulate the keyboard;
  • alternate pointing devices, which are used to simulate mouse pointing and clicking.
Accessible Description

An accessible description provides additional information, related to an interface element, that complements the accessible name. The accessible description might or might not be visually perceivable.

Accessible Name

The accessible name is the name of a user interface element. Each platform accessibility API provides the accessible name property. The value of the accessible name may be derived from a visible (e.g., the visible text on a button) or invisible (e.g., the text alternative that describes an icon) property of the user interface element. See related accessible description.

A simple use for the accessible name property may be illustrated by an "OK" button. The text "OK" is the accessible name. When the button receives focus, assistive technologies may concatenate the platform's role description with the accessible name. For example, a screen reader may speak "push-button OK" or "OK button". The order of concatenation and specifics of the role description (e.g., "button", "push-button", "clickable button") are determined by platform accessibility APIs or assistive technologies.

Tooltip attribute

Any host language attribute that would result in a user agent generating a tooltip such as in response to a mouse hover in desktop user agents.

RFC-2119 Keywords

RFC-2119 keywords are formatted in uppercase and in bold type font. When the keywords shown above are used, but do not share this format, they do not convey formal information in the RFC 2119 sense, and are merely explanatory, i.e., informative. As much as possible, such usages are avoided in this specification.

Normative and Informative Sections

The indication whether a section is normative or non-normative (informative) applies to the entire section including sub-sections.

Informative sections provide information useful to understanding the specification. Such sections may contain examples of recommended practice, but it is not required to follow such recommendations in order to conform to this specification.

Name and Description

The starting point of the name and description computation is a DOM [=element=]. The output is a flat, unstructured string that can be as simple as a single word, or a string of space-separated tokens. Examples include Save and Reload from disk.

An important factor is the [=element|element's=] role, that determines which content contributes to the name string. Roles have a nameFrom RDF property, with three possible values:

author
name is generated from values provided by the author in explicit markup features such as the aria-label and aria-labelledby [=attribute=], or a host language labeling mechanism, such as the alt or title [=attribute=] in HTML, or the desc [=element=] in SVG.
contents
name is generated from the Text [=nodes=] associated with the [=element=]. Although this may be allowed in addition to "author" in some roles, "content" is used only if higher priority "author" features are not provided. Priority is defined by the text equivalent computation algorithm.
prohibited
the element has no name. Authors MUST NOT use the aria-label or aria-labelledby attributes to name the element.

The Accessible Rich Internet Applications (WAI-ARIA) 1.2 [[!WAI-ARIA]] specification provides lists of roles that support name from author, roles that support name from content and roles that cannot be named.

Name Computation

User agents MUST compute an accessible name using the rules outlined below in the section titled Text Equivalent Computation.

Description Computation

The following table provides the order of precedence for markup that can be applied to compute an accessible description. User agents MUST use the first applicable entry from the table where the listed conditions are met, as described in the last column. The user agent MUST NOT use any markup other that the first relevant markup found, even if that markup results in an empty description:

Precedence Attribute Applicable conditions How used to compute description
1 aria-describedby attribute Use on any element Name computation on all nodes referenced by aria-describedby on the element, concatenated, and separated by a space character
2 aria-description attribute Use on any element As a flat string
3 host language features which participate in the description calculation Unique host language features MAY participate in the description computation for an element, only if they were not already used for the accessible name of the applicable element. See HTML AAM: Accessible Description Computation for the HTML elements which meet this condition. Either a text equivalent computation of the host language element, or the string value of the host language attribute.
4 host language tooltip attribute or equivalent feature (e.g., HTML title attribute)
  • Any element
  • Only use if not already used for the accessible name of this node
As a flat string

Text Equivalent Computation

The text equivalent computation is used by both the accessible name and accessible description. There are different rules provided for several different types of [=element|elements=], [=nodes=], and combinations of markup. Text alternatives are built up, when appropriate, from all the relevant content contained within an [=element=]. This is accomplished via steps 2B and 2F, which are recursive, using the full set of rules to retrieve text from its own children or nodes it references.

The purpose of the computation is to create a perceivable label or description for alternative presentations, in the form of a flat string of space separated textual tokens.

Terminology

Root node
The DOM [=nodes|node=] or [=element=] for which the text alternative is sought.
Current node
The DOM [=nodes|node=] currently traversed to compute the root node's text equivalent. Initially, the current node is the root node, but at later stages is either some descendant of the root node, or another referenced node.
Rendered child nodes
The [=nodes=] that are rendered as child nodes of a given node when taking [=shadow root|shadow roots=] and [=slot|slots=] into consideration.
Flat string
A string of characters where all carriage returns, newlines, tabs, and form-feeds are replaced with a single space, and multiple spaces are reduced to a single space. The string contains only character data; it does not contain any markup.
Total accumulated text
The text equivalent computed up to, but not including the current node.
Accumulated text
Text accumulated at a step or sequence of steps described below. It is temporary storage for those steps.
Result
The text equivalent computed at one of the steps described below.
Append the result, without a space, to X
  • If X is empty, copy the result to X.
  • If X is non-empty, copy the result to the end of X.
Append the result, with a space, to X
  • If X is empty, copy the result to X.
  • If X is non-empty, add a space to the end of X and then copy the result to X after the space.
Prepend result, without a space, to X
  • If X is empty, copy the result to X.
  • If X is non-empty, copy the result to the start of X.
Prepend the result, with a space, to X
  • If X is empty, copy the result to X.
  • If X is non-empty, copy the result to the start of X, and add a space after the copy.

Computation steps

The text alternative for a given element is computed as follows:

  1. Initialization: Set the root node to the given element, the current node to the root node, and the total accumulated text to the empty string (""). If the root node's role prohibits naming, return the empty string ("").
  2. Computation: Compute the text alternative for the current node:
    1. Hidden Not Referenced: If the current node is [=element/hidden=] and is:
      1. Not part of an aria-labelledby or aria-describedby traversal, where the node directly referenced by that relation was hidden.
      2. Nor part of a native host language text alternative element (e.g. label in HTML) or attribute traversal, where the root of that traversal was hidden.
      Return the empty string.

      It's important to clarify the broad definition of hidden for the purposes of accessible name calculation:

      1. Nodes with CSS properties display:none, visibility:hidden, visibility:collapse or content-visibility:hidden: They are considered hidden, as they match the guidelines "not perceivable" and "explicitly hidden".
      2. Nodes with CSS properties opacity:0 or filter:opacity(0%), or similar SVG mechanisms: They are not considered hidden. Text hidden with these methods can still be selected or copied, and user agents still expose it in their accessibility trees.
      3. Nodes with the aria-hidden="true" property: it is considered hidden, matching the "explicitly hidden" guideline.
      4. Nodes hidden off screen or behind another object: they are not considered hidden. They are exposed in the accessibility tree and they can even name on-screen objects.

      By default, assistive technologies do not relay hidden information, but an author can explicitly override that and include hidden text as part of the accessible name or accessible description by using aria-labelledby or aria-describedby.

    2. LabelledBy: Otherwise, if the current node has an aria-labelledby [=attribute=] that contains at least one valid IDREF, and the current node is not already part of an ongoing aria-labelledby or aria-describedby traversal, process its IDREFs in the order they occur:
      1. Set the accumulated text to the empty string.
      2. For each IDREF:
        1. Set the current node to the node referenced by the IDREF.
        2. LabelledBy Recursion: Compute the text alternative of the current node beginning with the overall Computation step. Set the result to that text alternative.
        3. Append a space character and the result to the accumulated text.
      3. Return the accumulated text if it is not the empty string ("").

      The result of LabelledBy Recursion in combination with Hidden Not Referenced means that user agents MUST include all nodes in the subtree as part of the accessible name or accessible description, when the node referenced by aria-labelledby or aria-describedby is hidden.

    3. Embedded Control: Otherwise, if the current node is a control embedded within the label (e.g. any element directly referenced by aria-labelledby) for another widget, where the user can adjust the embedded control's value, then return the embedded control as part of the text alternative in the following manner:
      1. Textbox: If the embedded control has role textbox, return its value.
      2. Combobox/Listbox: If the embedded control has role combobox or listbox, return the text alternative of the chosen option.
      3. Range: If the embedded control has role range (e.g., a spinbutton or slider):
        1. If the aria-valuetext property is present, return its value,
        2. Otherwise, if the aria-valuenow property is present, return its value,
        3. Otherwise, use the value as specified by a host language attribute.
    4. AriaLabel: Otherwise, if the current node has an aria-label [=attribute=] whose value is not undefined, not the empty string, nor, when trimmed of [=ascii whitespace|whitespace=], is not the empty string:
      1. If traversal of the current node is due to recursion and the current node is an embedded control, ignore aria-label and skip to rule Embedded Control.
      2. Otherwise, return the value of aria-label.
    5. Host Language Label: Otherwise, if the current node's native markup provides an [=attribute=] (e.g. alt) or [=element=] (e.g. HTML label or SVG title) that defines a text alternative, return that alternative in the form of a flat string as defined by the host language, unless the element is marked as presentational (role="presentation" or role="none").
      See HTML-AAM, SVG-AAM, or other host language documentation for more information on markup that defines a text alternative.

      For example, in HTML, the img element's alt attribute defines a text alternative string, and the label element provides text for the referenced form element. In SVG2, the desc and title elements provide a description of their parent element.

    6. Name From Content: Otherwise, if the current node's role allows name from content, or if the current node is referenced by aria-labelledby, aria-describedby, or is a native host language text alternative [=element=] (e.g. label in HTML), or is a descendant of a native host language text alternative [=element=]:
      1. Name From Content Reset: Set the accumulated text to the empty string.
      2. Name From Generated Content: Check for CSS generated textual content associated with the current node and include it in the accumulated text. The CSS ::before and ::after pseudo elements [[!CSS2]] can provide textual content for [=element|elements=] that have a content model.
        1. For ::before pseudo elements, User agents MUST prepend CSS textual content, without a space, to the textual content of the current node.
        2. For ::after pseudo elements, User agents MUST append CSS textual content, without a space, to the textual content of the current node.
      3. Determine Child Nodes: Determine the rendered child nodes of the current node:
        1. If the current node has an attached [=shadow root=], set the rendered child nodes to be the child nodes of the [=shadow root=].
        2. Otherwise, if the current node is a [=slot=] with [=slot/assigned nodes=], set the rendered child nodes to be the [=slot/assigned nodes=] of the current node.
        3. Otherwise, set the rendered child nodes to be the child nodes of the current node.
      4. Name From Each Child: For each rendered child node of the current node:
        1. Set the current node to the rendered child node.
        2. Compute the text alternative of the current node beginning with the overall Computation step. Set the result to that text alternative.
        3. Append the result to the accumulated text.
      5. Return the accumulated text if it is not the empty string ("").

      Important: Each [=nodes|node=] in the subtree is consulted only once. If text has been collected from a descendant, but is referenced by another IDREF in some descendant node, then that second, or subsequent, reference is not followed. This is done to avoid infinite loops.

      This step can apply to the child nodes themselves, which means the computation is recursive and results in text collected from all the elements in the current node's subtree, no matter how deep it is. However, any given descendant [=nodes|node's=] text alternative can result from higher precedent markup described in steps B through D above, where "Namefrom: author" attributes provide the text alternative for the entire subtree.

      18 January 2024: The ARIA Working Group is considering the feasibility of joining text strings with and without spaces, depending on the CSS display value of the current node, and its adjacent nodes and pseudo-elements. The ongoing discussion is in AccName #225.

    7. Text Node: Otherwise, if the current node is a Text [=Node=], return its textual contents.
    8. Recursive Name From Content: Otherwise, if the current node is a descendant of an element whose Accessible Name or Accessible Description is being computed, and contains descendants, proceed to Name From Content Reset.
    9. Tooltip: Otherwise, if the current node has a Tooltip attribute, return its value.

      Tooltip attributes are used only if nothing else, including subtree content, has provided results.

    10. Append a space character and the result of each step above to the total accumulated text.
  3. After all steps are completed, the total accumulated text is used as the accessible name or accessible description of the [=element=] that initiated the computation.

Accessible Name and Description Mapping

Information concerning name and description accessibility API mappings, including relationships, such as labelled-by/label-for and described-by/description-for, is documented in the Core Accessibility API Mappings specification [[!CORE-AAM-1.2]]. See the mapping table entries for aria-label, aria-labelledby, and aria-describedby.

Appendices

Change Log

Substantive changes since the last public working draft

Substantive changes since the Accessible Name and Description Computation 1.1 Recommendation

  • 27-June-2019: Add statement allowing for the possibility of naming being prohibited on the root node. Note: This change in and of itself has no implementation impact, but it allows other specifications to optionally prohibit naming for a top-level element. Furthermore, even if this prohibition is made within a specification, that prohibition will not have any impact on calculating name from contents.

Acknowledgments

The following people contributed to the development of this document.